The present invention relates to the electrode art. It finds particular application in conjunction with electrodes for stimulating skeletal muscles and will be described with particular reference thereto.
Functional restoration of a paralyzed limb can be achieved through the application of technique known as functional electrical stimulation (FES). In this technique, an electrode is implanted at an appropriate point in one of the patients skeletal muscles. The electrode must be positioned accurately, generally with a tolerance of a couple of millimeters. Once the electrode is implanted, its lead wire is run under tile skin to an exit site or connected to an implanted stimulator or other similar device.
Physiological movements are relatively complex, frequently requiring the coordinated operation of numerous muscles. To achieve full functional control, a patient may need as many as 50 or more implanted electrodes. The leads from the plurality of electrodes run through the tissue and the muscles to an exit site or are connected to an implanted stimulator or other similar device.
The skeletal muscle tissue environment is much more severe than the environment for brain electrodes, skin surface electrodes, heart electrodes, or the like. The stimulated skeletal muscle is continually contracting and expanding. The implanted electrode moves a relatively large distance with each expansion and contraction relative to movement which brain, skin, or heart electrodes undergo. One problem with the prior art electrodes has been a loosening of the electrodes due to the muscle contraction and expansion. Another significant problem with the prior art electrodes has been failure of the electrode leads attributable in large part to the flexing and stress which they undergo during muscle contraction and expansion.
Once the electrodes are implanted and the leads are run under the skin, it is difficult to tell when a lead or electrode has failed. More specifically, electrical continuity of the lead is commonly checked by placing a current into the electrode lead at the interface and completing the circuit with an electrode on the surface of the patient's skin. The patient's muscle, skin, and other tissue between the surface electrode and the implanted electrode has a relatively high impedance. Frequently, it is difficult to distinguish between the high impedance attributable to an electrical break in the lead from the high impedance of the patient tissue.
The present invention contemplates a new electrode and lead combination which overcomes the above-referenced problems and others.